The present invention relates to novel multimeric configurations and forms of intercellular adhesion molecule (ICAM), including both full length and truncated forms of these proteins, that effectively bind to human rhinovirus and can effectively reduce HRV infectivity.
Full length ICAM, also known as human rhinovirus receptor (HRR), is termed transmembrane ICAM (tmICAM-l); non-transmembrane ICAM forms, also known as truncated ICAM (tICAM), are less than full length. When in a multimeric configuration, preferably as dimers, these proteins display enhanced binding of human rhinovirus (HRV) and are able to reduce HRV infectivity. In addition, these multimerized proteins may also be used to reduce infectivity of other viruses that are known to bind to the `major` group human rhinovirus receptor (HRR), such as coxsackie A virus, and may also be used to block transmembrane intra-cellular adhesion molecule (tmICAM) interaction with lymphocyte function-associated antigen-1 (LFA-1) critical to many cell adhesion processes involved in the immunological response. Lastly, these multimerized proteins may be used to study the ICAM-1/HRV interaction especially with respect to designing other drugs directed at affecting this interaction.
Human rhinoviruses are the major causative agent of the common cold. They belong to the picornavirus family and can be classified based on the host cell receptor to which they bind. Tomassini, et al., J. Virol., 58: 290 (1986) reported the isolation of a receptor protein involved in the cell attachment of human rhinovirus. Approximately 90% of the more than 115 serotypes of rhinoviruses, as well as several types of coxsackie A virus, bind to a single common receptor termed the "major" human rhinovirus receptor (HRR); the remaining 10% bind to one or more other cell receptors.
Recently, Greve, J. et al., Cell, 56:839 (1989), co-authored by the co-inventors herein, identified the major HRR as a glycoprotein with an apparent molecular mass of 95,000 daltons and having an amino acid sequence essentially identical to that deduced from the nucleotide sequence of a previously described cell surface protein named intercellular adhesion molecule (ICAM-1). Simmons, D. et al., Nature, 331:624 (1988). Staunton, et al., Cell, 52:925-933 (1988). Subsequently, Staunton, D. E., et al., Cell, 56:849 (1989), confirmed that ICAM-1 is the major surface receptor for HRV. See also, Staunton, et al., Cell, 61:243-254 (1990).
ICAM-1 (number according to Staunton et al., 1988) is an integral membrane protein 505 amino acids long [SEQ ID NO: 1, encoded by nucleotides 138-1653 of SEQ ID NO:2] and has: i) five immunoglobulin-like extracellular domains at the amino-terminal end (amino acid residues 1-453), ii) a hydrophobic transmembrane domain (454-477), and iii) a short cytoplasmic domain at the carboxy-terminal end (478-505). ICAM-1 is a member of the immunoglobulin supergene family and functions as a ligand for the leukocyte molecule, lymphocyte function associated molecule-1 (LFA-1), a member of the integrin family. Heterotypic binding of LFA-1 to ICAM-1 mediates cellular adhesion of diverse cell types and is important in a broad range of immune interactions; induction of ICAM-1 expression by cytokines during the inflammatory response may regulate leukocyte localization to inflammatory sites. The primary structure of ICAM-1 has been found to be homologous to two cellular adhesion molecules, i.e., neural cell adhesion molecule (NCAM) and mylein-associated glycoprotein (MAG).
Several approaches to decreasing infectivity of viruses in general, and of rhinovirus in particular, have been pursued including: i) developing antibody to the cell surface receptor for use in blocking viral binding to the cell, ii) using interferon to promote an anti-viral state in host cells; iii) developing various agents to inhibit viral replication; iv) developing antibodies to viral capsid proteins/peptides; and v) blocking viral infection with isolated cell surface receptor protein, that specifically blocks the viral binding domain of the cell surface receptor.
Using this latter approach, Greve, et al., Cell, 56:879 (1989), supra, reported that purified tmICAM-1 could bind to rhinovirus HRV3 in vitro. Unpublished results with HRV2, HRV3, and HRV14 demonstrate a positive correlation between the ability to bind to rhinovirus and the ability to neutralize rhinovirus particularly if the binding studies are carried out under conditions where ICAM-1 is presented in a particular form and configuration as discussed further, infra. Results (unpublished) using HRV14 and HRV2 demonstrate a positive correlation between the receptor class of the virus and the ability to bind to tmICAM-1 in vitro. That is, ICAM-1, being the major receptor, can bind to HRV3, HRV4, and other "major" receptor serotypes and neutralize them, while it does not bind or neutralize HRV2, a "minor" receptor serotype. Further studies (unpublished), using purified tmICAM-1, demonstrate that it effectively inhibits rhinovirus infectivity in a plaque-reduction assay when the rhinovirus is pretreated with tmICAM-1 (50% reduction of titer at 10 nM receptor and one log reduction of titer at 100 nM receptor protein). These data were consistent with the affinity of rhinovirus for ICAM-1 of Hela cells, which had an apparent dissociation constant of 10 nM, and indicated a direct relationship between the ability of the receptor to bind to the virus and to neutralize the virus.
Because large-scale production of tmICAM-1 is not presently economically feasible, and because maintenance of tmICAM-1 in an active form requires the use of detergents, alternate means of producing a receptor protein for use as a rhinovirus inhibitor are desirable. Forms of the tmICAM-1 cDNA gene have been developed (as well as cell lines that produce the expression products; U.S. Ser. No. 390,662, now abandoned) that have been genetically altered to produce truncated ICAM-1 molecules. These truncated forms of ICAM-1 (tICAM(453) and tICAM(185)) lack the transmembrane region and are secreted into the cell culture medium. They bind to rhinovirus in the assay described in Greve, et al., Cell, 56:879 (1989), supra, although at substantially reduced levels relative to tmICAM-1. Thus, their effectiveness as inhibitors of rhinoviral infectivity appeared to be less than that of tmICAM-1. See generally co-pending applications, U.S. Ser. No. 130,378, now abandoned; U.S. Ser. No. 262,570; U.S. Ser. No. 262,428, now abandoned; U.S. Ser. No. 239,571, now abandoned; and U.S. Ser. No. 390,662, now abandoned.
U.S. Ser. No. 239,571 filed Sep. 1, 1988 and its CIP applications U.S. Ser. No. 262,428, now abandoned and U.S. Ser. No. 390,662, now abandoned are directed to the use of transmembrane rhinovirus receptor as an inhibitor of rhinovirus infectivity using non-ionic detergent to maintain the transmembrane protein in solution and directed to truncated intercellular adhesion molecules (tICAM) having extracellular domains 1, 2, 3, 4, and 5 of transmembrane intercellular adhesion molecules (tmICAM) and which truncated forms do not require the presence of non-ionic detergent for solubilization;
U.S. Ser. No. 130,378 filed Dec. 8, 1987 and its CIP application U.S. Ser. No. 262,570, now abandoned are directed to transfected cell lines which express the major rhinovirur receptor (HRR) and to the indentification of HRR as intercellular adhesion molecule; and
U.S. Ser. No. 301,192, now U.S. Pat. No. 5,235,049 filed Jan. 24, 1989 and its CIP application U.S. Ser. No. 449,356, abandoned are directed to a naturally occurring soluble ICAM (sICAM) related to but distinct from tmICAM in that this sICAM lacks the amino acids spanning the transmembrane region and the cytoplasmic region; in addition this sICAM has a novel sequence of 11 amino acids at the C-terminus.
Subsequently, Marlin, S.D., et al., Nature, 344:70 (1990), reported the construction and purification of a truncated soluble form of the normally membrane bound ICAM-1 molecule which they termed sICAM-1. It has both the transmembrane domain and the cytoplasmic domain of the protein deleted and differs from the wild-type amino acid sequence by a single conservative substitution at its carboxyl end. It is composed of residues 1-452 of ICAM-1 and of a novel phenylalanine residue at the C-terminus. These workers demonstrated that sICAM-1 was required at levels &gt;50 .mu.g/ml to prevent the binding of HRV14 virus to cells. However, they also found that sICAM-1 at 1 .mu.g/ml (18 nM), when continually present in the culture medium, was able to inhibit by 50% the progression of an infection by HRV54. The inhibitory activity was correlated with the receptor class of the virus, in that coxsackie A13 but not poliovirus or HRV2 was inhibited; infectivity data for HRV14 was not reported, however. Thus, they did not demonstrate a direct correlation between binding and inhibition of infectivity. Further, as discussed in greater detail, infra, attempts to reproduce the results obtained by Marlin, et al. have not been successful and have suggested that a higher concentration of the truncated form of ICAM (10-fold higher than transmembrane ICAM) is required to produce a 50% reduction in viral titer.
To date, no one has been able to demonstrate an agent that binds to and effectively reduces infectivity of human rhinovirus (by blocking viral infection with isolated cell surface receptor protein) as effectively as tmICAM-1; accordingly there continues to exist a need in the art for a form of ICAM-1 that can effectively bind to human rhinovirus and can effectively reduce HRV infectivity.